Timing synchronization between nodes in a network is described in various standards such as IEEE 1588-2008 “Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems,” ITU-T G.8265.1/Y.1365.1 (07/14) “Precision time protocol telecom profile for frequency synchronization,” ITU-T G.8275.1 “Time and Phase Profile,” the contents of each is incorporated by reference herein. The requisite information for the transfer of precise time is (1) a time reference point, or “significant instant” to which timing information can be related, (2) the timing information itself, and (3) a measure of the delay it takes to transfer the timing information between two nodes. The transfer of time over optical networks can be challenging because of the delays introduced by elastic First-In-First-Out (FIFOs) required in transport mapping schemes such as OTN and enhanced high coding gain soft decision Forward Error Correction (SD-FEC) schemes. Uncertainty in these delays (at start-up, or after fault recovery) results in uncertainty in the transferred time. Also, variability and uncertainty in these delays results in time error in between the network nodes.
IEEE 1588-2008 is referred to as Precision Time Protocol (PTP) and is used to synchronize clocks throughout the network. IEEE 1588-2008 only defines a protocol for transferring time information over a packet network. It does not address performance aspects such as the time accuracy that can be achieved over a network. In general, PTP supports accuracy in the sub-microsecond range. ITU-T defines performance aspects of Ethernet telecom networks, but to date, has not defined performance aspects for OTN networks. Based on current 100 GB/s system designs, measurements have shown that the optical transport equipment can contribute hundreds of nanoseconds of time uncertainty over a single network hop. Measurements of some off-the-shelf components have shown much worse performance. The ITU-T is currently developing standards to address the shortcomings of time transfer over OTN networks. However, these newly developed standards will not address the time uncertainty and jitter that can be introduced by SD-FEC type of schemes added on the line side in optical modem/Digital Signal Processing (DSP) devices, as these schemes and devices have non-deterministic timing therein.